Field of the Invention
The present invention relates to a wax dispersant for a toner and a toner including the wax dispersant for a toner.
Description of the Related Art
In recent years, electrophotographic full-color copiers have become widely used and also started to be applied in the printing market. The printing market requires high speed, high image quality, and high productivity as well as adaptability to a wide range of media (paper-types).
One concrete example of such requirements is “media isokinetic ability” in which, even when a paper type is changed from thick to thin, it is possible to perform continuous printing without changing the process speed for matching the paper type or changing the set heating temperature of a fixing device.
From the standpoint of this media isokinetic ability, a toner is required to ensure that fixing could be appropriately completed within a wide range of fixing temperature from a low temperature to a high temperature.
A method for imparting releasability to a toner by including a wax in the toner is used to fix a toner appropriately within a wide range of fixing temperature. In this case, it is desirable that the wax in the toner be in a fine and uniformly dispersed state because the quality of the dispersed state has a significant impact on toner properties.
Japanese Patent Application Laid-open No. 2011-13548 suggests a technique of including a wax dispersant in a toner in order to control the dispersed state of the wax in the toner.
Further, Japanese Patent Application Laid-open No. 2007-264349 suggests using a toner binder configured of a high-viscosity resin, a low-viscosity resin, and a dispersant so as to increase the dispersivity of a wax and thereby suppress image degradation.
However, even in the case where the dispersed state of a wax in a toner is controlled, if the toner is left to stand at a high temperature and high humidity, charging performance of the toner may be degraded because the wax elutes to the toner surface and toner flowability may therefore be worsened.
Further, Japanese Patent Application Laid-open No. 2011-123352 suggests a variety of toners, in which low-temperature fixing performance is improved by adding to the toner a crystalline resin having sharp melt property, thereby enabling fixing in a wide temperature range.
However, in high-speed machines adapted to the printing market, there are cases where fixability at a low temperature is still insufficient and leaving the toner at a high temperature may lead to blocking. Further, since the toner shape is not controlled, transfer efficiency can be insufficient.
In this respect, Japanese Patent Application Laid-open No. 2013-15830 suggests controlling the toner shape by heat treatment and lowering the adhesion force of the toner in order to increase the transfer efficiency.
Here, although the heat treatment controls the toner shape, this process is known to cause waxes having high adhesivity to elute to the vicinity of the toner surface. As a result, the flowability of the toner is degraded under the effect of the wax having eluted to the vicinity of the toner surface, and charging performance of the toner may deteriorate.
It follows from the above that there is still room for investigation aimed at controlling the dispersed state of a wax in a toner while ensuring charging performance, low-temperature fixability, and blocking resistance of the toner.